Because of the poor biodegradability of petroleum-based fluids, elevated petroleum cost and the finite supply of petroleum, there is a growing interest in using vegetable oils for industrial applications. For example, soybean oil (SBO) has been used as a lubricant SBO is bio-degradable. This reduces disposal cost and long-term liability risks, especially in applications where lubricants are lost directly into the environment (1). Furthermore, the low toxicity and high flash point of SBO create a safer working environment for operators. SBO has better anti-wear properties, high viscosity index and low acidity; SBO is more protective to equipment and performs equally well or sometimes even better than traditional petroleum-based oils. A vegetable-based crankcase oil containing 10% to 20% SBO was tested in automobiles, and its performance was reported to meet industry standards. A 1970 Ford Mustang logged more than 26,000 miles with no breakdowns using a crankcase oil containing SBO (2). Biosoy, a hydraulic fluid made from SBO, has been tested in various equipment including garbage trucks and city buses since 1995, and its anti-wear properties for the high-pressure hydraulic systems meet or exceed conventional hydraulic fluid requirements (3, 4).
The use of many vegetable oils in the applications described above has a drawback due to their susceptibility to rapid oxidization. The oxidation causes a polymerization of the triglycerides and increases the viscosity dramatically, thus severely shortening the life of SBO-based lubricants and hydraulic fluids. Researchers have tried various ways to solve this problem, including developing oleate-enriched soybean lines (5) and concentrating oleate in ordinary SBO by urea fractionation. Ruger and Harnmond (6) tested the effectiveness of antioxidants to prevent viscosity increase in SBO at 105xc2x0 C. (typical temperature condition during industrial use of a lubricant) with bubbling air in the presence of colloidal iron and copper metal. Several antioxidants tested were effective in preventing viscosity increase in SBO with tertiary butylhydroquinone (TBHQ) working the best. Addition of citric acid slightly enhanced the effectiveness of TBHQ. Other antioxidants, especially those that are more effective than TBHQ in preventing oxidization and hence polymerization and viscosity increase in vegetable oils, are desirable.
The present invention provides new compounds that can be used as antioxidants for either molecules that do not contain ester groups or esters of alcohols that contain two or more ester groups per molecule wherein at least two of the ester groups are on adjacent carbons in the alcohol moiety. The above molecules for which the new compounds of the present invention can act as antioxidants are referred to as target molecules in the specification. Copper ions can enhance the antioxidization activity of the new compounds. One can add one of the new compounds and optionally, a copper-containing compound, into an industrial fluid containing a target molecule to inhibit the oxidization of the target molecule. Compositions that contain one of the new compounds and optionally, a copper-containing compound, are within the scope of the present invention. Industrial fluids that contain a target molecule, one of the new compounds and optionally, copper ions, are also within the scope of the present invention.
It is an advantage of the present invention that the new compounds in combination with copper ions are more effective than most other antioxidant systems in inhibiting the oxidization of target molecules.
Other objects, advantages, and features of the present invention will become apparent from the following detailed description of the invention.